Fin material and heat exchanger

ABSTRACT

A heat-exchanger fin material ( 1 ) has a coating film ( 3 ) formed on at least one surface of an aluminum substrate ( 2 ). An outermost surface of the coating film ( 3 ) is a positively-chargeable coating ( 31 ) that is essentially composed of only one or more resins selected from the group consisting of cellulose-based resins, acrylic-based resins, vinyl alcohol-based resins, acrylamide-based resins, and ester-based resins. The surface roughness Ra of the coating film ( 3 ) is 100 nm or less. A heat exchanger ( 5 ) includes a plurality of fins composed of the fin material ( 1 ) and at least one metal tube ( 7 ) passing through the plurality of fins ( 1 ).

CROSS-REFERENCE

This application is the US national stage of International PatentApplication No. PCT/JP2017/005971 filed on Feb. 17, 2017, which claimspriority to Japanese Patent Application 2016-033395 filed on Feb. 24,2016.

TECHNICAL FIELD

The present invention generally relates to a fin material for use in aheat exchanger and to a heat exchanger that uses the same.

BACKGROUND ART

Fin-tube-type heat exchangers are used in, for example, indoor units andoutdoor units of air conditioners. Such heat exchangers typicallycomprise metal tubes, through which a coolant flows, and numerous finsmade of aluminum, through which the metal tubes pass. Ahydrophilic-coating material or a water-repellent coating material isprecoated on both sides of the fins, such that the fins have a coatingfilm on both surfaces thereof.

Various contaminants, such as dust, soot, and tobacco tar, adhere to thesurfaces of the fins of a heat exchanger during operation. To deal withthis problem, a method that prevents the adhesion of such contaminantsand a method that facilitates the removal of adhered contaminants areknown. Specifically, a method is known that prevents the adhesion ofhydrophilic contaminants, such as dust, due to static electricity by,for example, coating an antistatic agent on the fin surfaces. Inaddition, a method is known that makes it easy to remove lipophiliccontaminants, such as soot, by coating an oil-repellent fluororesin onthe fin surfaces. However, there is a need in the art for furtherimprovement in adhesion-prevention effects against positively chargedcontaminants, such as dust.

For example, in Patent Document 1, a technique is described thatprevents the adhesion of tar components of tobacco by setting theabsolute value of the amount of triboelectric charge of asurface-coating film of an electrically insulating substrate to 0-200 V.In addition, a fin having a hydrophilic blended film, which includeshydrophobic particles, formed thereon is described, for example, inPatent Document 2.

PRIOR ART LITERATURE Patent Documents

Patent Document 1

PCT International Publication No. WO 2006/134808

Patent Document 2

Japanese Laid-open Patent Publication 2009-229040

SUMMARY OF THE INVENTION

However, in Patent Document 1, electric charge on a metal substrate thatis generated by friction is easily dissipated. In addition, in PatentDocument 2, although an attempt was made to inhibit the adhesion ofhydrophobic and hydrophilic contaminants by using a blended film thatincludes a hydrophilic component and a hydrophobic component, there wasa problem in that hydrophobic contaminants tend to adhere to thehydrophobic component, and hydrophilic contaminants tend to stick to thehydrophilic component. In particular, there is a tendency for positivelycharged contaminants, such as dust, to adhere to the fins of a heatexchanger. In addition, uncharged contaminants also tend to adhere.Consequently, there is a need in the art for improvement in the adhesioninhibition and removability of such contaminants.

In view of one or more of these circumstances, aspects of the presentteachings concern a heat-exchanger fin material that excels inadhesion-inhibiting effects and removability of contaminants, such asdust, and a heat exchanger that uses the same.

In one aspect of the present teachings, a heat-exchanger fin materialpreferably comprises:

a substrate composed of aluminum; and

a coating film formed on at least one surface of the substrate, thecoating film being composed of a coating having one layer or two or morelayers;

wherein an outermost surface of the coating film is apositively-chargeable coating;

the positively-chargeable coating is essentially composed of only one ormore resins selected from the group consisting of cellulose-basedresins, acrylic-based resins, vinyl alcohol-based resins,acrylamide-based resins, and ester-based resins; and

the surface roughness Ra of the coating film is 100 nm or less.

In another aspect of the present teachings, a heat exchanger comprises afin composed of the above-described heat-exchanger fin material.

The above-described heat-exchanger fin material (hereinbelow, called“fin material” where appropriate) has, on its outermost surface, thepositively-chargeable coating essentially composed of the resinsdescribed above. A positively-chargeable coating composed only of suchspecified resins tends to become positively charged upon contact (byfriction) with air. Furthermore, because the above-mentioned resins thatconstitute the coating of the outermost surface are electricallyinsulating, they hold charge well. Consequently, if a positively chargedcontaminant, such as dust, approaches the surface of the coating film(which has the positively-chargeable coating on the outermost surfacethereof), a repulsive force acts between the positively chargedcoating-film surface and the positively charged contaminant, andtherefore the contaminant tends not to adhere.

In addition, owing to the fact that the surface roughness Ra of thecoating film is 100 nm or less and the coating film excels in surfacesmoothness, contaminants tend not to adhere for this reason as well.Consequently, not only do positively charged contaminants tend not toadhere, but also uncharged contaminants tend not to adhere. Furthermore,even if a contaminant adheres, the contaminant is easily washed away bycondensed water or the like that adheres to the coating-film surface ofthe fin material, for example, during operation of the heat exchangerwhen the condensed water flows off the fin. In this regard, it is notedthat, if condensed water adheres to the coating-film surface of the finmaterial, then the amount of charge on the surface temporarily decreasesand becomes zero. However, even though it becomes easier forcontaminants to adhere to the wetted surface, adhered contaminants areeasily washed away in the manner described above. Furthermore, when thecoating-film surface dries, the positively-chargeable coating will thencarry positive charges once again, such that the adhesion-inhibitingeffects against contaminants, such as dust, are exhibited once again.

In addition, a positively-chargeable coating composed only of the resinsdescribed above excels not only in hydrophilic properties but also inhydrophilicity durability. Consequently, condensed water easilypenetrates between the coating and any contaminants adhered thereto,such that contaminants adhered to the surface are easily washed away.

As was mentioned above, in a heat exchanger comprising the fins composedof the above-mentioned fin materials, the fins can exhibit excellentadhesion-inhibiting effects and removability of contaminants.Furthermore, they also excel in hydrophilic properties andhydrophilicity durability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a fin material, which has asubstrate and a positively-chargeable coating, according to workingexample 1.

FIG. 2 is an explanatory diagram that shows a water-contact angleaccording to working example 1.

FIG. 3 is an explanatory diagram that shows inhibition of the adhesionof contaminants to a surface of the fin material according to workingexample 1.

FIG. 4A shows, according to working example 1, a cross-sectional view ofthe fin material having a chemical-conversion coating or a primer layerbetween the substrate and a coating film; FIG. 4B shows across-sectional view of the fin material having a coating-film layercomprising a positively-chargeable coating as well as another coating,such as a corrosion-resistant coating.

FIG. 5 is a schematic diagram of a heat exchanger according to workingexample 2.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of a fin material and a heat exchanger using the same willnow be explained. The fin material comprises a substrate composed ofaluminum. In the present specification, “aluminum” is a general term fora metal or an alloy in which aluminum is the principal constituent andis a general concept that includes pure aluminum and aluminum alloys.

A coating film formed on the substrate includes a coating having onelayer or two or more layers. A coating formed by a single application ofone coating material is one layer; furthermore, a coating that is formedby multiple applications of a coating material in which the compositionis the same for each application is also one layer. The coating film hasa positively-chargeable coating on its outermost surface.

Examples of resins that form the positively-chargeable coating arecellulose-based resins, acrylic-based resins, vinyl alcohol-basedresins, acrylamide-based resins, and ester-based resins. At least one ofthese can be used. These resins have a carboxy group or a hydroxy groupas the functional group.

The positively-chargeable coating is essentially composed only of theresins described above; it does not contain, for example, silica-basedor titanium-based inorganic particles, water-soluble resins, or thelike; it may contain unavoidable impurities, such as a resincross-linking agent (e.g., a metal compound such as a Zr compound). Asdescribed above, the positively-chargeable coating is essentiallycomposed of at least one resin selected from the group consisting ofcellulose-based resins, acrylic-based resins, vinyl alcohol-basedresins, acrylamide-based resins, and ester-based resins. The content ofthese resins in the positively-chargeable coating is preferably 99 mass% or more and more preferably 99.5 mass % or more.

The surface of the positively-chargeable coating will positively chargeupon contact (by friction) with air. The surface electrical potential ofthe positively-chargeable coating varies depending on the type of resinin the positively-chargeable coating, the composition, the filmthickness, the surface roughness, and the like and is within a range of,for example, +0.01 V to +10 V. In addition, the absolute value of thesurface electrical potential varies not only in accordance with thecoating but also with the external environment, such as the temperatureand the humidity of the air.

The thickness of the positively-chargeable coating is preferably 0.1-6μm. In this case, the positive charge on the positively-chargeablecoating is more readily retained, and surface smoothness is more easilyincreased. From the same viewpoint, the thickness of thepositively-chargeable coating is preferably 0.3-3 μm and more preferably0.5-1.5 μm.

The coating film may have another coating in addition to thepositively-chargeable coating. An example of such a coating is acorrosion-resistant coating composed of, for example, a urethane-basedresin, an epoxy-based resin, or the like. Even if the coating film hasanother coating, the coating of the outermost surface is thepositively-chargeable coating described above.

In addition, a primer layer may be formed between the coating film andthe substrate. Thereby, adhesion between the substrate and the coatingfilm can be further improved. The primer layer can be formed of at leastone type selected from the group consisting of a urethane-based primer,an acrylic-based primer, and an epoxy-based primer.

In addition, a chemical-conversion coating may be formed between thecoating film and the substrate or between the primer layer and thesubstrate. Adhesion between the coating film and the substrate oradhesion between the primer layer and the substrate can be improved bythe chemical-conversion coating. The chemical-conversion coating can beformed by subjecting the aluminum substrate to a phosphate-chromatetreatment, a phosphate-zirconium treatment, a boehmite treatment, or thelike.

The surface roughness Ra of the coating film on the fin material ispreferably 100 nm or less. If the surface roughness Ra is more than 100nm, then uncharged contaminants and the like tend to adhere and,furthermore, adhered contaminants tend not to come off. The surfaceroughness Ra of the coating film is preferably 50 nm or less and morepreferably 20 nm or less. The surface roughness of the coating film isan arithmetic-mean roughness Ra as stipulated in JIS B0601-2001. Thesurface roughness Ra of the coating film can be controlled by adjustingthe thickness of the coating film, the surface roughness of thesubstrate, and the like.

The contact angle of water on the surface of the coating film ispreferably 40° or less. In this case, the surfaces of the fin materialcan sufficiently exhibit excellent hydrophilic properties. In addition,both immediately after the manufacture of a fin material, as well asafter the repeated immersion in water and drying according to the agingprocedure described below, the water-contact angle on the coating-filmsurface is, as described above, preferably 40° or less and morepreferably 30° or less.

Fin materials are used in the manufacture of the heat exchanger as, forexample, described below. Specifically, first, a coil-shaped finmaterial is cut to prescribed dimensions, and thereby a plurality ofsheet-shaped fins is obtained. Subsequently, the fins are subject toslit (hole) formation, louver molding, and collar formation using apress. Next, the fins are arranged such that they are stacked in thestate in which they are spaced apart from one another by a prescribedspacing while metal tubes, which are disposed at prescribed locations,are passed through holes provided in the fins. Subsequently,tube-expanding plugs are inserted into the metal tubes to enlarge theouter diameter of the metal tubes, and thereby the metal tubes and thefins are caused to closely contact each other. Thus, the heat exchangercan be obtained. The heat exchanger can be used in, for example, anindoor unit or an outdoor unit of an air conditioner.

WORKING EXAMPLES Working Example 1

In the present example, multiple fin materials (specifically, sample E1to sample E13 and sample C1 to sample C7) pertaining to working examplesand comparative examples were prepared, and their characteristics werecompared and evaluated. As shown in FIG. 1, a fin material 1 accordingto the working examples comprises: a substrate 2 composed of aluminum;and a coating film 3 formed on the surface(s) thereof. The coating film3 comprises a positively-chargeable coating 31, which is essentiallycomposed of at least one resin selected from the group consisting ofcellulose-based resins, acrylic-based resins, vinyl alcohol-basedresins, acrylamide-based resins, and ester-based resins. The surfaceroughness Ra of the coating film 3 is 100 nm or less. The substrate 2 isan aluminum sheet having a sheet thickness of 0.1 mm as stipulated inJIS A 1050-H26. It is noted that the fin material of the comparativeexample has a configuration that is the same as the working examples,except that the composition and surface roughness of the coating filmdiffer, as shown in Table 1, which is discussed below.

The fin materials 1 of the samples were manufactured by applying coatingmaterials, which contained the resin components of the compositionsshown in Table 1 (discussed below), onto the substrates, thereby formingthe coating films 3. Each coating film 3, i.e., thepositively-chargeable coating 31, in the present example was formeddirectly on the substrate 2. In the manufacture of sample C7, a coatingmaterial containing a resin component and silica particles was used(refer to Table 1). It is noted that, in Table 1, CMC indicatescarboxymethyl cellulose, PAA indicates polyacrylic acid, PAM indicatespolyacrylamide, PVA indicates polyvinyl alcohol, PES indicatespolyester, EPO indicates polyepoxy, PU indicates polyurethane, and PEGindicates polyethylene glycol.

As the surface roughness Ra of the coating film 3 for each of thesamples, the arithmetic-mean roughness Ra according to JIS B0601-2001was measured using a probe-type, surface-roughness measuring instrument(specifically, the scanning probe microscope JSPM-5200 made by JEOL®Ltd.) compliant with JIS B0651-2001. The visual field during measurementwas 25 μm×25 μm. For each sample, arbitrary visual fields were selectedat ten locations, the measurement described above was performed at eachlocation, and the arithmetic mean of these ten locations was taken asthe surface roughness Ra.

Next, the surface electrical potential of the coating film of eachsample in the dry state was measured as follows, and the results areshown in Table 1. The measurements were performed using the scanningprobe microscope (i.e., SPM) JSPM-5200 made by JEOL® Ltd. Specifically,a bias voltage was applied between the probe of the scanning probemicroscope and an arbitrary location of the coating-film surface, andthe surface electrical potential was calculated based on the change infrequency when the bias voltage was changed. The measuring method, thecalculating method, and the like were in accordance with the manual ofthe JSPM-5200 made by JEOL® Ltd. For each sample, the surface electricalpotential was measured at ten locations, and the arithmetic-mean valuethereof is shown in Table 1. It is noted that the surface electricalpotentials shown in the table are representative values, and it wasconfirmed that, even for the same sample, variations arise in themeasurement values due to external factors and the like, such astemperature and humidity. However, inversion of positive or negative inthe charged state of the surface did not occur.

TABLE 1 Surface Film Surface Potential Sample Roughness Ra ThicknessComponent Content Component Content Component Content Surface of CoatingFilm No. [nm] [μm] 1 [mass %] 2 [mass %] 3 [mass %] Charge [V] E1 50 1CMC 100 — — — — + +0.5 E2 10 1 CMC 100 — — — — + +0.5 E3 20 1 CMC 100 —— — — + +0.5 E4 100 1 CMC 100 — — — — + +0.5 E5 50 0.1 CMC 100 — — — — ++0.01 E6 50 6 CMC 100 — — — — + +10 E7 50 1 PAA 100 — — — — + +5 E8 50 1PAM 100 — — — — + +8 E9 50 1 PVA 100 — — — — + +10 E10 50 1 PES 100 — —— — + +2 E11 50 1 PVA 90 PES 10 — — + +8 E12 50 1 CMC 75 PAA 25 — — + +6E13 50 1 CMC 75 PAA 20 PAM 5 + +7 C1 50 1 EPO 100 — — — — − −10 C2 50 1CMC 50 PU 50 — — − −4 C3 120 1 CMC 100 — — — — + +0.5 C4 150 7 CMC 100 —— — — + +15 C5 150 1 CMC 50 PEG 50 — — + +0.25 C6 50 1 PU 100 — — — — −−8 C7 150 1 CMC 50 Silica particles 50 — — + +8

For each sample, evaluations of the hydrophilic properties, thecontamination-adhesion properties, the contamination-removingproperties, corrosion resistance, and moisture resistance were performedas below. The results thereof are shown in Table 2.

(1) Hydrophilic Properties

After the manufacture of each sample, the initial water-contact anglewas measured. Specifically, as shown in FIG. 2, a water droplet 19having a volume of 2 μl was dropped onto the coating film 3 of the finmaterial 1 of each sample. Then, the contact angle α of the waterdroplet 19 on the coating film 3 was measured. This was taken as theinitial water-contact angle. Next, each sample was aged, and thewater-contact angle α was measured again after the aging. Specifically,aging was performed by repeating a cycle, in which every sample wasimmersed in ion-exchanged water for 2 min and then dried by air blowingfor 6 min, 300 times. Subsequently, the water-contact angle after theaging was measured. This was taken as the post-aging water-contactangle. In addition, each sample was subjected to a contaminationtreatment, and the water-contact angle α was measured again.Specifically, the samples were placed inside a sealed bottle togetherwith a contaminant composed of a higher fatty acid such that thecontaminant and the samples were not in contact with one another. Theinterior of the sealed bottle was then heated to a temperature of60-100° C., whereby the higher fatty acid inside the sealed bottle wasvaporized and some of the contaminant adhered to the coating-filmsurface of the samples. This state was maintained for a long time(specifically, 100 hours), and then the temperature inside the bottlewas cooled to room temperature while the sealed state was maintained.Then, the fin materials of the samples were taken out of the bottle, andthe water-contact angles α were measured again. If the contact angle αwas 30° or less, then the sample was evaluated as “excellent”; if thecontact angle α was more than 30° and 40° or less, then the sample wasevaluated as “satisfactory”; and if the contact angle α was more than40°, then the sample was evaluated as “unsatisfactory.”

(2) Contamination-Adhesion Properties

The contamination-adhesion properties were evaluated by assessing theadhesion of electrically charged dust and electrically conductive dustto the coating-film surface of each sample. Specifically, theelectrically charged dust and the electrically conductive dust were eachblown against the surface of the coating film of each sample via air.Subsequently, the amount of the electrically charged dust and the amountof the electrically conductive dust adhered to the coating-film surfacewere each measured. The measurements of the adhered amounts wereperformed by measuring the weight of each sample before and after thedust was blown against each sample, calculating the amount of adhereddust of each sample based on the weight difference, and then convertingthe weight difference into the amount of adhered dust per unit of area.If the adhered amount of the electrically charged dust was less than 0.2g/m², then the sample was evaluated as “excellent”; if the adheredamount of the electrically charged dust was 0.2 g/m² or more and 0.5g/m² or less, then the sample was evaluated as “satisfactory”; and ifthe adhered amount of the electrically charged dust was more than 0.5g/m², then the sample was evaluated as “unsatisfactory.” The evaluationof the adhered amount of the electrically conductive dust was alsoperformed in the same manner. It is noted that Kanto loam dust, which isa powder stipulated in JIS Z8901-2006, was used as the electricallycharged dust, and carbon black, which is a powder stipulated in JISZ8901-2006, was used as the electrically conductive dust.

(3) Contamination Removability

Contamination removability was evaluated by assessing removability ofelectrically charged dust and electrically conductive dust from thecoating-film surface of each sample. Specifically, as in the evaluationof contamination-adhesion properties described above, samples wereprepared by adhering electrically charged dust and electricallyconductive dust to the coating-film surfaces. Next, each sample wascooled to a prescribed temperature by cooling the surface on theopposite side that the dust is adhered to, thereby causing condensedwater to form on the surface having the adhered dust. Then, the state inwhich condensed water formed and flowed off was maintained for aprescribed period of time. Subsequently, the surfaces of each samplewere sufficiently dried, after which the amount of the remaining dustthat was not removed by the condensed water was measured in the samemanner as the evaluation of the adhesion properties described above. Ifthe residual amount of each dust was less than 0.1 g/m², then the samplewas evaluated as “excellent”; if the residual amount of each dust was0.1 g/m² or more and less than 0.5 g/m², then the sample was evaluatedas “satisfactory”; and if the residual amount of each dust was 0.5 g/m²or more, then the sample was evaluated as “unsatisfactory.”

(4) Corrosion Resistance

Using each sample, the salt spray test stipulated in JIS Z2371 wasperformed for 500 hours, and post-test corrosion resistance wasevaluated. Observation was performed visually; after the test, if thesurface of the coating film did not whiten, then the sample wasevaluated as “excellent”; if part of the surface whitened, then thesample was evaluated as “satisfactory”; and if the entire surfacewhitened, then the sample was evaluated as “unsatisfactory.”

(5) Moisture Resistance

Using each sample, the moisture-resistance test stipulated in JIS H4001was performed for 960 hours, and post-test moisture resistance wasevaluated. Observation was performed visually; after the test, if thesurface of the coating film did not whiten, then the sample wasevaluated as “excellent”; if part of the surface whitened, then thesample was evaluated as “satisfactory”; and if the entire surfacewhitened, then the sample was evaluated as “unsatisfactory.”

TABLE 2 Hydrophilic Properties Initial Post-Aging Water WaterContamination-Adhesion Properties Contamination Removability ContactContact Post-Aging Electrically Electrically Sample Angle AngleHydrophilic Electrostatic Conductive Electrostatic Conductive CorrosionMoisture No. [°] [°] Properties Dust Dust Dust Dust ResistanceResistance E1 15 33 Satisfactory Satisfactory Satisfactory SatisfactorySatisfactory Satisfactory Satisfactory E2 18 36 SatisfactorySatisfactory Excellent Satisfactory Satisfactory Satisfactory ExcellentE3 17 36 Satisfactory Satisfactory Excellent Satisfactory SatisfactorySatisfactory Excellent E4 12 37 Satisfactory Satisfactory SatisfactorySatisfactory Satisfactory Satisfactory Satisfactory E5 22 38Satisfactory Satisfactory Satisfactory Satisfactory SatisfactorySatisfactory Satisfactory E6 15 32 Satisfactory SatisfactorySatisfactory Satisfactory Satisfactory Excellent Excellent E7 18 36Excellent Satisfactory Excellent Satisfactory Satisfactory SatisfactoryExcellent E8 20 36 Satisfactory Satisfactory Excellent SatisfactorySatisfactory Satisfactory Excellent E9 34 37 Satisfactory SatisfactorySatisfactory Satisfactory Satisfactory Satisfactory Satisfactory E10 1838 Satisfactory Satisfactory Satisfactory Satisfactory SatisfactorySatisfactory Satisfactory E11 30 40 Satisfactory SatisfactorySatisfactory Satisfactory Satisfactory Excellent Excellent E12 20 28Excellent Satisfactory Satisfactory Satisfactory Satisfactory ExcellentSatisfactory E13 20 27 Excellent Satisfactory Satisfactory SatisfactorySatisfactory Satisfactory Satisfactory C1 40 65 UnsatisfactoryUnsatisfactory Satisfactory Unsatisfactory Satisfactory SatisfactorySatisfactory C2 20 40 Unsatisfactory Unsatisfactory SatisfactoryUnsatisfactory Satisfactory Satisfactory Satisfactory C3 10 37Satisfactory Satisfactory Unsatisfactory Satisfactory UnsatisfactorySatisfactory Satisfactory C4 10 40 Satisfactory SatisfactoryUnsatisfactory Satisfactory Unsatisfactory Satisfactory Satisfactory C520 35 Unsatisfactory Satisfactory Satisfactory UnsatisfactorySatisfactory Satisfactory Satisfactory C6 60 80 UnsatisfactoryUnsatisfactory Satisfactory Unsatisfactory Satisfactory SatisfactorySatisfactory C7 25 30 Unsatisfactory Satisfactory UnsatisfactorySatisfactory Unsatisfactory Satisfactory Satisfactory

As can be understood from Table 1 and Table 2, each fin material havingthe positively-chargeable coating on its outermost surface, which, as insample E1 to sample E13, is essentially composed only of one or moreresins selected from the group consisting of cellulose-based resins,acrylic-based resins, vinyl alcohol-based resins, acrylamide-basedresins, and ester-based resins, excels in thecontamination-adhesion-inhibition effect. This is because, as shown inFIG. 3, the surface of the positively-chargeable coating 31 ispositively charged by contact with air, and therefore the adhesion ofpositively charged dust 91 and the like can be inhibited. In addition,because the surface roughness of the coating film 3 of sample E1 tosample E13 is 100 nm or less and the samples excel in surfacesmoothness, the adhesion of uncharged dust 92 and the like also can beinhibited. Furthermore, because dusts 91, 92 adhered to the surface ofthe smooth coating film 3 are easily washed away by condensed water orthe like, they also excel in contamination removability.

The surface of each positively-chargeable coating 31 in sample E1 tosample E13 is positively charged upon contact (by friction) with air, asdescribed above. If condensed water or the like adheres to thepositively-chargeable coating 31, then the surface electrical potentialdecreases and becomes zero, but it carries a positive charge once againupon drying and contact with air. Charging by this drying and the chargedissipation by the condensed water are reversible and performedrepeatedly.

In addition, the sample E1 to sample E13 also excel in hydrophilicproperties and in post-aging hydrophilic properties (i.e.,hydrophilicity durability). Furthermore, they also excel inpost-contamination hydrophilic properties. In addition, they also excelin corrosion resistance and moisture resistance.

In contrast, the surface of the sample C1, which has a coating composedof an epoxy resin as the coating film, the surface of the sample C2,which has a coating that contains both carboxymethyl cellulose andpolyurethane as the coating film, and the surface of the sample C6,which has a coating composed of polyurethane as the coating film, arenegatively charged by contact with air. Consequently, the adhesionproperties with respect to contaminants, such as dust, the removabilityof contaminants, and the like were insufficient. In particular, theadhesion properties and removability of positively charged electricallycharged dust were poor. In addition, the hydrophilicproperties—particularly the post-aging hydrophilicity durability and thepost-contamination hydrophilicity durability—of sample C1 to sample C6were also insufficient. The post-contamination hydrophilicity durabilitywas also insufficient for sample C2.

In addition, with regard to sample C3 and sample C4, in which thesurface roughness Ra of the coating film was large and the smoothnesswas insufficient, the adhesion properties, the removability, etc. ofcontaminants, such as electrically conductive dust, were insufficient.In addition, with regard to sample C5, which contains a water-solubleresin, such as PEG, in the coating, the removability of electricallycharged dust and the like were insufficient. Furthermore, thepost-contamination hydrophilicity durability was also insufficient. Inaddition, the post-contamination hydrophilicity durability of sample C7,which has silica particles in the coating, was insufficient.Furthermore, the surface roughness of sample C7, which has the silicaparticles, became large and, as in sample 3 and sample 4, the adhesionproperties, the removability, etc. of contaminants, such as electricallyconductive dust, were insufficient.

In the present example, although a fin material was described in whichthe coating film 3, which comprises the positively-chargeable coating31, was formed directly on the substrate 2, as shown in FIG. 1, the finmaterial may have at least one of a chemical-conversion coating 41 and aprimer layer 42 between the substrate 2 and the coating film 3, whichcomprises the positively-chargeable coating 31, as shown in FIG. 4A. Inaddition, as shown in FIG. 4B, the outermost surface of the coating film3 should have the positively-chargeable coating 31 and furthermore mayhave a corrosion-resistant coating 32.

Working Example 2

Working example 2 is a heat exchanger comprising fins composed of thefin materials of working example 1. As shown in FIG. 5, the heatexchanger 5 is a cross-fin-tube type and comprises: numeroussheet-shaped fins 6, each composed of the fin material 1, and metaltubes 7 that pass through these and are for transferring heat. The fins6 are spaced apart by a prescribed spacing and are disposed in parallel.The width of each plate fin is, for example, 25.4 mm; the height is, forexample, 290 mm; the fin-stacking pitch is, for example, 1.4 mm; and thewidth of the entire heat exchanger is, for example, 300 mm. The heightdirection of the fin 6 is the rolling-parallel direction of thesubstrate. There are two columns of the metal tube 7 in the width of thefins, and there are 14 stages of the metal tube 7 in the fin height. Itis noted that, for simplicity of illustration, several of the metaltubes 7 are not shown in FIG. 5. In addition, the metal tube is a coppertube having a helical groove on its inner surface. The dimensions of themetal tube are outer diameter: 7.0 mm, bottom-wall thickness: 0.45 mm,fin height: 0.20 mm, fin vertical angle: 15.0°, and helix angle: 10.0°.

Each of the heat exchangers 5 was prepared as follows. First, assemblyholes (not shown), each having a fin-collar part with a height of 1-4 mmfor inserting the metal tubes 7 therethrough and fixing such, wereformed by press working the fins 6, each composed of the fin material 1.After stacking the plate fins 6, the separately prepared metal tubes 7were inserted through the assembly holes. A copper tube having a grooveformed on its inner surface by rolling or the like was cut to a standardlength and hairpin bent, to form the metal tubes 7. Next, by insertingtube-expanding plugs into one end of the metal tubes 7 and widening theouter diameter of the metal tubes 7, the metal tubes 7 were secured tothe plate fins 6. After the tube-expanding plugs were removed, U-benttubes were joined, by braising, to the metal tubes 7, and thereby eachof the heat exchangers 5 was obtained.

By using samples E1-E13 according to working example 1 as the finmaterials 1, contaminants, such as dust, tend not to adhere to the fins6 of the heat exchanger 5 and, even if these contaminants adhere, theyare easily removed by condensed water or the like. Furthermore, the fins6 also excel in hydrophilic properties, hydrophilicity durability, andthe like.

1. A heat-exchanger fin material comprising: a substrate composed ofaluminum; and a coating film formed on at least one surface of thesubstrate and composed of a coating having one layer or two or morelayers; wherein the coating film has a positively-chargeable coating onits outermost surface; the positively-chargeable coating is essentiallycomposed of only at least one resin selected from the group consistingof cellulose-based resins, acrylic-based resins, vinyl alcohol-basedresins, acrylamide-based resins, and ester-based resins; and the surfaceroughness Ra of the coating film is 100 nm or less.
 2. Theheat-exchanger fin material according to claim 1, wherein the surfaceroughness Ra of the coating film is 50 nm or less.
 3. The heat-exchangerfin material according to claim 1, wherein the surface roughness Ra ofthe coating film is 20 nm or less.
 4. The heat-exchanger fin materialaccording to claim 1, wherein the water-contact angle on the surface ofthe coating film is 40° or less.
 5. The heat-exchanger fin materialaccording to claim 1, wherein the water-contact angle on the surface ofthe coating film is 30° or less.
 6. The heat-exchanger fin materialaccording to claim 1, wherein the film thickness of thepositively-chargeable coating is 0.1-6 μm.
 7. A heat exchangercomprising: a fin composed of the heat-exchanger fin material accordingto claim
 1. 8. The heat-exchanger fin material according to claim 3,wherein: the water-contact angle on the surface of the coating film is30° or less, and the film thickness of the positively-chargeable coatingis 0.1-6 μm.
 9. The heat-exchanger fin material according to claim 8,wherein the film thickness of the positively-chargeable coating is0.5-1.5 μm.
 10. The heat-exchanger fin material according to claim 9,wherein at least 99 mass % of the positively-chargeable coating iscomposed of one or more of carboxymethyl cellulose, polyacrylic acid,polyacrylamide, polyvinyl alcohol, and/or polyester.
 11. A fincomprising: a substrate composed of pure aluminum or an aluminum alloy;and a coating film formed on at least one surface of the substrate andcomposed of a coating having one layer or two or more layers; wherein anoutermost layer of the coating film consists essentially of one or moreresins selected from the group consisting of cellulose-based resins,acrylic-based resins, vinyl alcohol-based resins, acrylamide-basedresins, and ester-based resins; and the coating film has an averagesurface roughness Ra of 100 nm or less.
 12. The fin according to claim11, wherein: the coating film exhibits a water-contact angle of 40° orless, and the coating film has a thickness of 0.1-6 μm.
 13. The finaccording to claim 12, wherein the average surface roughness Ra of thecoating film is 50 nm or less.
 14. The fin according to claim 13,wherein at least 99 mass % of the outermost layer of the coating film iscomposed of one or more compound(s) selected from the group consistingof carboxymethyl cellulose, polyacrylic acid, polyacrylamide, polyvinylalcohol, and polyester.
 15. The fin according to claim 13, wherein atleast 99.5 mass % of the outermost layer of the coating film is composedof one or more compound(s) selected from the group consisting ofcarboxymethyl cellulose, polyacrylic acid, polyacrylamide, polyvinylalcohol, and polyester.
 16. The fin according to claim 15, wherein thecoating film has a surface electric potential of +0.01 V to +10 V. 17.The fin according to claim 16, wherein the thickness of the coating filmis 0.5-1.5 μm.
 18. The fin according to claim 17, wherein: the coatingfilm exhibits a water-contact angle of 30° or less, and the averagesurface roughness Ra of the coating film is 20 nm or less.
 19. A heatexchanger comprising: a plurality of fins according to claim 18; and ametal tube passing through holes in the plurality of fins and in contactwith the plurality of fins.
 20. A heat exchanger comprising: a pluralityof fins according to claim 11; and a metal tube passing through holes inthe plurality of fins and in contact with the plurality of fins.